1. Field of the Invention
The present invention concerns an x-ray apparatus according to the preamble of the type having a cooling device for cooling the anode through which a fluid coolant flows.
2. Description of the Prior Art
X-ray tubes with a high load capacity are conventionally used in the field of x-ray computed tomography. These can be either x-ray tubes with a rotary anode as are known, for example, from DE 40 12 019 B4 or U.S. Pat. No. 5,541,975 or rotating envelope tubes as they are, for example, known from DE 103 35 664 B3. Cooling devices for dissipation of the heat generated in the anode are provided. In rotary anodes the cooling device extends in an anode shaft (fashioned hollow) and/or in the anode plate (fashioned hollow). In rotating envelope tubes a vacuum housing embodying the anode is surrounded by the cooling device. An electrically-insulating oil or a thermally insulating oil typically flows through the cooling device as a coolant. In addition to the property of electrical isolation, thermally insulating oil can be used given a working temperature of 200° C. due to its relatively high boiling point. However, insulating oil disadvantageously exhibits only a relatively low heat capacity, meaning the heat accumulating at the anode cannot be dissipated particularly efficiently with such insulating oil. Apart from this the insulating oil is highly mobile. A durable, complete sealing of the cooling device can be realized only with difficulty in practice. To overcome this disadvantage it has been proposed according to U.S. Pat. No. 5,541,975 to use liquid metal as a coolant, but this is expensive and complicated.